Boffins spin a solid state qubit in a nucleus

Reliable quantum memory in silicon

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A group of researchers from the University of New South Wales has produced a functioning solid-state qubit with a read-out fidelity of 99.8 percent, taking the world another step along the path towards a functioning quantum computer.

The team used the magnetic spin of the phosphorus nucleus as the basis for their experiment, published in Nature on April 18 (US time). They claim that accuracy rivals the 2012 Nobel-awarded “ion trap” – a single atom trapped in a vacuum chamber.

According to Associate Professor Andrea Morello from the School of Electrical Engineering and Telecommunications at UNSW, the team used magnetic resonance – as used in MRI scans – to “control and read-out the nuclear spin of a single atom in real time.”

The weak magnetic field of a phosphorus atom, they explain, exists either as “up” or “down”, or, in the quantum world, as a superposition of both. This experiment was about storage, rather than superposition: the information was stored by controlling the up-down direction of the nucleus' magnetic spin.

The big advance, the team claims, is that this experiment doesn't need the vacuum chamber of the ion trap. Instead, Morello explains, the phosphorus atom is “in a silicon chip that can be wired up and operated electrically like normal integrated circuits.”

In a previous experiment, the group had manipulated a whole atom; this time, they're working with the nucleus only. While the nucleus is harder to work with – it only occupies a millionth of the atom's diameter – it's also nearly immune from disturbances from the outside world.

“Our nuclear spin qubit can store information for longer times and with greater accuracy. This will greatly enhance our ability to carry out complex quantum calculations once we put many of these qubits together”, explained UNSW PhD student Jarryd Pla, lead experimental author of the paper. ®